1. Field of the Invention
The present invention relates to a selective oxygen-permeable substrate, a positive electrode for a metal-air battery, a metal-air battery, and a selective oxygen-permeable membrane. More specifically, the present invention relates to a selective oxygen-permeable substrate capable of selectively introducing oxygen in the air into the inside and having high durability against an electrolytic solution. Further, the present invention relates to a positive electrode for a metal-air battery provided with the selective oxygen-permeable substrate and to a metal-air battery provided with the positive electrode for a metal-air battery. Furthermore, the present invention relates to a selective oxygen-permeable membrane capable of selectively permeating oxygen in the air and having high durability against an electrolytic solution.
A metal-air battery has a very large discharge capacity per “unit mass of positive-electrode active material” because metal is used as a negative-electrode active material and because oxygen is used as the positive-electrode active material. In recent years, increase in capacity and output of a battery has been required for electric automobiles, mobile devices, etc., and raising performance of the metal-air battery has been expected.
As described above, since the positive-electrode active material of the metal-air battery is oxygen, oxygen in the air can be used as the positive-electrode active material. However, if the air is introduced into the metal-air battery as it is, carbon dioxide in the air is also introduced therein. Since carbon dioxide may react with the electrolytic solution used in the metal-air battery to deteriorate the battery performance, it is desirable to inhibit carbon dioxide from being introduced into the metal-air battery. Thus, there was a problem of introduction of carbon dioxide into the metal-air battery in the case of using oxygen in the air as the positive electrode of the metal-air battery though it is preferable that carbon dioxide is not introduced into the positive electrode of the metal-air battery.
2. Description of Related Art
In order to solve such a problem, there is studied a method where an oxygen permeable polymer membrane is attached to the positive electrode of a metal-air battery or a fuel battery to selectively take in oxygen from the air by the oxygen permeable polymer membrane (see, e.g., JP-A-5-62687, JP-A-7-105991, and JP-A-7-14565).
On the other hand, there is studied an oxygen permeable polymer membrane capable of concentrating oxygen contained in the air (see, e.g., JP-A-11-262643 and JP-A-2003-53125).
In the air batteries described in JP-A-5-62687, JP-A-7-105991, and JP-A-7-14565, since a polymer membrane is used as the oxygen permeable membrane, there is room for further improving the durability against the electrolytic solution.
In the oxygen permeable polymer membranes described in JP-A-11-262643 and JP-A-2003-53125, since a polymer membrane is used as the oxygen permeable membrane, there is room for further improving the durability against the electrolytic solution.